Gardnerville residents will have one last chance to see the revised flood hazard maps for Pine Nut Creek and Cottonwood and Martin sloughs before the revisions are shipped off to the Federal Emergency Management Agency.
Manhard Consulting, along with town and county staff, will answer questions and provide input 6-8 p.m. Thursday in the county administrative building, 1616 Eighth St. in Minden.
"It's important to let citizens know that they're potentially in a flood hazard, though they may not be mapped in that hazard now," said Manhard hydrologist/engineer Denny Peters. "We don't want to surprise anyone."
Manhard estimates that the Pine Nut Creek drainage peaks at about 4,300 cubic feet per second in a 100-year event, versus FEMA's existing estimate of about 5,600 cfs. But the re-study also accounts for downstream flows of Pine Nut not included in FEMA's models. The new maps show portions of Chichester Estates in the "AE" and "AO" 100-year flood zones, which require insurance, and a vast swath of the subdivision in the shaded-X 500-year zone, which does not require insurance.
Manhard estimates Cottonwood Slough's peak flow, where it splits off the east fork of the Carson River, at about 6,000 cfs in a 100-year event, lower than FEMA's 7,050 cfs. They also estimate 100-year peak flows much lower where Cottonwood Slough splits into Martin Slough at Lampe Park.
Peters said FEMA assumed a percentage split of 3,900 cfs continuing down Cottonwood Slough and about 3,250 cfs in Martin Slough. Accounting for irrigation ditches and other flow "break-out areas" upstream, he put those numbers at about 2,200 cfs in Cottonwood Slough after Lampe, and only about 400 cfs in Martin Slough.
If FEMA doesn't approve the new maps, Peters said, then nothing changes.
"FEMA is generally in favor of mapping efforts with more parcels in the flood hazard than removed," he said. "We do both in this. We simultaneously put parts of Chichester in the hazard zone while removing considerable properties from the flood zones along Cottonwood and Martin sloughs. Again the primary purpose of all this is to let citizens know potential flood hazards. If it changes, and they're in the flood zone, then we need to let them know. If it changes, and they're not, then there's no need to pay insurance."
The proposed maps are available for download at www.gardnerville-nv.gov. For more information, contact town manager/engineer Tom Dallaire at 782-7134.
